Ionization and Attraction of Neutral Molecules to a Charged Spacecraft.
AEROSPACE CORP EL SEGUNDO CA SPACE SCIENCES LAB
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Neutral molecules given off by spacecraft outgassing or thrusters may become ionized by solar uv radiation or ambient energetic electrons. These ions may be reattracted to the spacecraft and hence constitute a source of contamination for sensitive spacecraft surfaces. In this report, the magnitude of this effect is calculated. Comparable fluxes of ions are found to be produced by uv radiation and by electrons. It is predicted that 0.02 percent of the heavy neutral spacecraft effluents will be ionized within the spacecraft plasma sheath, and all of these will be returned to a negatively charged spacecraft. Using the best available outgas fluxes, it is also predicted that the reattraction of outgas products will be a significant contaiminating effect during the initial several months of the spacecrafts orbital lifetime, second only to direct contaminant impingement. Together these effects deposite 100 A of contaminants in the first 6 months. The ionizationreattraction mechanism cannot be ruled out on the basis of present data. The implications of assuming that this contamination mechanism is the dominant one during the early spacecraft lifetime are examined. In addition, a list of parameters that need to be measured more accurately is presented, and ways to combat contamination from this source are outlined.
- Unmanned Spacecraft